(1) Field of the Invention
The present invention relates to a data erasure method for a multilayer optical disc having multiple data layers and to an optical disc apparatus.
(2) Description of the Related Art
For the purpose of increasing the storage capacity of optical discs, multilayer optical discs, which each have a laminate structure of multiple data layers, are now being developed. For example, Blu-ray discs (BD), which enable high-density recording, can now have a total storage capacity of up to 400 GB by having 16 data layers each with a storage capacity of 25 GB. Increasing the number of data layers of an optical disc necessitates consideration of how to secure writing/reading capabilities for farther (or deeper) data layers from the light-incident surface of the disc and how to erase data from multiple data layers efficiently. For example, when data is erased from one data layer at a time, the data erasure time increases in proportion to the number of data layers.
For the purpose of initializing (i.e., erasing all data from) a multilayer disc in substantially the same amount of time as in initialization of a single-layer disc, Japanese Unexamined Patent Application Publication No. H09-91700 (Patent Document 1) discloses methods for simultaneously performing initialization on all the data layers by simultaneously radiating laser light onto all the data layers. Disclosed as its light radiation means are multiple optical heads (and multiple objective lenses) that are provided for the respective data layers and each radiate light (see Embodiments 1, 2 and 3). Further disclosed as the light radiation means is a single optical head (and a single objective lens) that radiates light onto multiple data layers with its focal depth being increased (see Embodiment 4).